According to a report today on Digital Music News, users of Spotify tend not to purchase music. This is hardly surprising since streaming is clearly a substitute to buying physical discs.
With the exception of aggregated rights owners (the record labels and publishers), and a handful of hugely successful artists, streaming is a revenue killer. It's bad news for most recording artists.
But then, for most artists selling records has never been a reliable way to make a dollar. The need to diversify their business through touring, merchandise, and whatever new media emerges in the coming decade, will remain true for most.